Cosmology and extragalactic astronomy Mat Page Mullard Space Science Lab, UCL Revision Lecture

Recap of everything! Galaxies: –Classification+Structure –Dark Matter Hubbles law – redshift and distance indicators Cosmological Principles, Olberss Paradox Cosmic microwave background –results and implications Inflation Nucleosynthesis, baryogenesis

Galaxies and dark matter Hubbles tuning fork diagram Spirals + barred spirals –Sa: large bulge, tight arms. –Sc: small bulge, loose arms Star formation, gas and dust in arms Density wave model Rotation, rotation curve -> dark matter MACHOs, WIMPs, how they are detected M o

Galaxies and dark matter Ellipticals E0-E7, En where n=10(1-b/a) Classified according to view from Earth Old, red stars (no star formation) little gas, little dust M o

Lenticulars (S0) –like spirals but no arms, just disc Irregulars –tend to be small, no definite structure

Where are the galaxies and how did they form? –Galaxies form in dark matter haloes –Most of the galaxies in rich clusters are ellipticals –bottom up vs. top down –hierarchical model - ellipticals built up by merging of disc galaxies –spirals created when galaxies accrete gas (with angular momentum) from the intergalactic medium

Massive accreting black holes in galactic nuclei. 90% are radio quiet, but can be identified by their strong emission lines. Most quasars are seen at large redshifts (z>0.3) Quasars

Hubbles law

Cosmic distance ladder

Cosmic microwave background:

Inflation What is it? –A period of rapid expansion in the early Universe –Caused by a state change as the Universe cools Why do we need it? –The horizon problem –large scale structure –flatness –the monopole problem

Olberss paradox Night sky should be infinitely bright! Solution: –The Universe is only 14 billion years old! –Light from stars more distant than 14 billion light years has not have reached us yet. –There is a limit to the size of the Universe which can illuminate the night sky. –The sky is allowed to be dark.

Finally: Good luck to you all!